As a dielectric composition used for a multilayer ceramic capacitor bulk shaped capacitor materials, such as lanthanum titanate (La2O3.2TiO2), zinc titanate (ZnO.TiO2), magnesium titanate (MgTiO3), titanium oxide (TiO2), bismuth titanate (Bi2O3.2TiO2), calcium titanate (CaTiO3) and strontium titanate (SrTiO3), are known. Capacitor materials of this kind have a small temperature coefficient, so that they can be preferably used for a coupling circuit, audio circuit and an image processing circuit, etc.
However, capacitor materials of this kind have a tendency that the permittivity becomes low (for example, less than 40) when the temperature coefficient becomes small (for example, within ±100 ppm/° C.), while when the permittivity becomes high (for example 90 or higher), the temperature coefficient also becomes large (for example, ±750 ppm/° C. or larger). For example, temperature coefficients (the reference temperature is 25° C., the unit is ppm/° C.) of La2O3.2TiO2, ZnO.TiO2, MgTiO3 are small as +60, −60 and +100, respectively, and along therewith, the permittivity (a measurement frequency is 1 MHz, no unit) becomes small as 35 to 38, 35 to 38 and 16 to 18, respectively. On the other hand, for example, permittivity of TiO2, Bi2O3.2TiO2, CaTiO3 and SrTiO3 is high as 90 to 110, 104 to 110, 150 to 160 and 240 to 260, respectively, and along therewith, their temperature coefficients become large as −750, −1500, −1500 and −3300, respectively. Accordingly, development of a temperature compensating capacitor material, which can maintain a relatively high permittivity even when the temperature coefficient is small, is desired.
In recent years, in the field of electronic devices, there have been demands for a furthermore compact capacitor element as an essential circuit element in a variety of electronic circuits along with electronic circuits becoming higher in density and more highly integrated.
For example, a thin film capacitor using a single-layer dielectric thin film is behind in making a compact integrated circuit with a transistor or other active element, which has been a factor of hindering realization of an ultra-high integrated circuit. It was a low permittivity of a dielectric material to be used that has hindered attaining of a compact thin film capacitor. Accordingly, it is significant to use a dielectric material having a high permittivity to realize a more compact thin film capacitor with a relatively high capacity.
Also, in recent years, a conventional multilayer film of SiO2 and Si3N4 has become hard to respond to a capacitor material for a DRAM of the next generation (gigabit generation) in terms of capacity density, and a material system having a higher permittivity has gathered attention. In such a material system, an application of TaOx (ε=30 or smaller) has been mainly studied but development of other materials has come to be actively pursued.
As a dielectric material having a relatively high permittivity, (Ba, Sr)TiO3 (BST) and Pb(Mg1/3 Nb2/3)O3 (PMN) are known.
It can be considered that it is possible to attain a compact body when composing a thin film capacity element by using a dielectric material of this kind.
However, a dielectric material of this kind was not a temperature compensating material and the temperature coefficient was large (for example, exceeding 4000 ppm/° C. in BST), so that when configuring a thin film capacitor element by using such a material, temperature characteristics of the permittivity was deteriorated in some cases. Also, when using dielectric materials of this kind, the permittivity declined as the dielectric film became thinner in some cases. Furthermore, a leakage property and a breakdown voltage were also deteriorated due to apertures generated on the dielectric film as the film became thinner in some cases. Furthermore, it was liable that the dielectric film to be formed had poor surface smoothness. Note that due to a large effect by lead compounds, such as PMN, on the environment, a high capacity capacitor not containing lead has been desired in recent years.
On the other hand, to realize a more compact multilayer ceramic capacitor with a larger capacity, it is desired that a thickness of one dielectric layer is made as thin as possible (a thinner layer) and the number of dielectric layers at a predetermined size is increased as much as possible (an increase of stacked layers).
However, for example, when producing a multilayer ceramic capacitor by a sheet method (a method of forming a dielectric green sheet layer on a carrier film by using a dielectric layer paste by the doctor blade method, etc., printing an internal electrode layer paste to be a predetermined pattern thereon, then, releasing them one by one and stacking the same), the dielectric layer could not be made thinner than ceramic material powder. Furthermore, it was difficult to make the dielectric layer thin, for example, as 2 μm or thinner because of problems of short-circuiting and breaking of internal electrode, etc. due to a defective dielectric layer. Also, when a thickness of one dielectric layer was made thinner, the number of stacked layers was also limited. Note that the same problem remained in the case of producing a multilayer ceramic capacitor by the printing method (a method of alternately printing a dielectric layer paste and an internal electrode layer paste for a plurality of times on a carrier film, for example, by using the screen printing method, then, removing the carrier film).
Due to the above reasons, there was a limit in making the multilayer ceramic capacitor more compact and higher in capacity.
Thus, a variety of proposals have been made to solve the problem (for example, the patent article 1: the Japanese Patent Publication No. 56-144523, the patent article 2: the Japanese Patent Publication No. 5-335173, the patent article 3: the Japanese Patent Publication No. 5-335174, the patent article 4: the Japanese Patent Publication No. 11-214245 and the patent article 5: the Japanese Patent Publication No. 2000-124056, etc.). These publications disclose methods of producing a multilayer ceramic capacitor formed by alternately stacking dielectric thin films and electrode thin films by using a variety of thin film forming methods, such as the CVD method, evaporation method and sputtering method.
However, in the techniques described in these patent articles, there is no description on composing a dielectric thin film by using a dielectric material having a small temperature coefficient and capable of maintaining a relatively high permittivity, and a temperature compensating thin film multilayer capacitor is not disclosed.
Also, a dielectric thin film formed by the methods described in the patent articles had poor surface smoothness, and short-circuiting of electrodes arose when stacking too much, so that those having 12 or 13 stacked layers or so were able to be produced at most. Therefore, even when the capacitor could be made compact, a higher capacity could not be attained without deteriorating temperature characteristics of permittivity.
Note that as described in the non-patent article 1 [“Particle Orientation for Bismuth Layer-Structured Ferroelectric Ceramic and Application to its Piezoelectric and Pyroelectric Material” by Tadashi Takenaka, pp. 23 to 77 in chapter 3 of Kyoto University Doctor of Engineering Thesis (1984)], it is known that a bulk bismuth layer-structured compound dielectric obtained by the sintering method is composed of a composition expressed by a composition formula of (Bi2O2)2+(Am−1 Bm O3m+1)2− or Bi2Am−1 Bm O3m+3, wherein “m” is a positive number from 1 to 8, “A” is at least one element selected from Na, K, Pb, Ba, Sr, Ca and Bi, and “B” is at least one element selected from Fe, Co, Cr, Ga, Ti, Nb, Ta, Sb, V, Mo and W.
However, in this article, nothing was disclosed on under what condition (for example, a relationship of a substrate surface and a c-axis orientation degree of a compound) when making the composition expressed by the above composition formula thinner (for example 1 μm or thinner), a thin film having excellent temperature characteristics of permittivity, capable of giving a relatively high permittivity and a low loss, having an excellent leakage property, improved breakdown voltage, and excellent surface smoothness even when made to be thin could be obtained.
Also, as disclosed in the patent article 6 (PCT/JP02/08574), the present inventors have developed “a thin film capacity element composition containing a bismuth layer-structured compound having a c-axis oriented vertically with respect to a substrate surface, wherein:
the bismuth layer-structured compound is expressed by a composition formula of (Bi2O2)2+(Am−1 Bm O3+1)2− or Bi2Am−1 Bm O3m+3, wherein “m” is an even number, “A” is at least one element selected from Na, K, Pb, Ba, Sr, Ca and Bi, and “B” is at least one element selected from Fe, Co, Cr, Ga, Ti, Nb, Ta, Sb, V, Mo and W” and filed before.
The present inventors furthermore pursued experiments and found that a thin film capacity element composition composed of a bismuth layer-structured compound having a specific composition included in claims of the patent article 6 but not described in an embodiment of the specification had particularly excellent temperature characteristics of capacitance and that it was possible to control the temperature characteristics, and completed the present invention.